Wind turbine blade provided with surface mounted device

ABSTRACT

A wind turbine blade ( 10, 610 ) for a rotor of a wind turbine ( 2 ) having a substantially horizontal rotor shaft is described. A surface mounted device ( 70, 70′, 170, 270, 370, 470, 570, 670, 770 ) is attached to a surface of the wind turbine blade ( 10 ). The surface mounted device ( 70, 70′, 170, 270, 370, 470, 570, 670, 770 ) is attached to the surface of the wind turbine blade ( 10, 610 ) via at least a first attachment part ( 77, 77 ′), which is connected to a part of the surface mounted device ( 70, 70′, 170, 270, 370, 470, 570, 670, 770 ). The attachment part ( 77, 77 ′) comprises a flexible housing ( 80, 80′, 680, 780 ) that forms a cavity ( 81, 81′, 681, 781 ) between at least the housing ( 80, 80′, 680, 780 ) and the surface of the wind turbine blade ( 10, 610 ). The cavity ( 80, 80′, 680, 780 ) is filled with an adhesive that provides an adhesive bonding to the surface of the wind turbine blade ( 10, 610 ).

TECHNICAL FIELD

The invention relates to a wind turbine blade provided with a surfacemounted device, and a method of attaching a device to a surface of awind turbine blade.

BACKGROUND ART

Ideally, a wind turbine blade of the airfoil type is shaped similar tothe profile of an aeroplane wing, where the chord plane width of theblade as well as the first derivative thereof increase continuously withdecreasing distance from the hub. This results in the blade ideallybeing comparatively wide in the vicinity of the hub. This again resultsin problems when having to mount the blade to the hub, and, moreover,this causes great loads during operation of the blade, such as stormloads, due to the large surface area of the blade.

Therefore, over the years, the construction of blades has developedtowards a shape, where the blade consists of a root region closest tothe hub, an airfoil region comprising a lift-generating profile furthestaway from the hub and a transition region between the root region andthe airfoil region. The airfoil region has an ideal or almost idealblade shape with respect to generating lift, whereas the root region hasa substantially circular cross-section, which reduces the storm loadsand makes it easier and safer to mount the blade to the hub. The rootregion diameter is preferably constant along the entire root region. Dueto the circular cross-section, the root region does not contribute tothe energy production of the wind turbine and, in fact, lowers this alittle because of drag. As it is suggested by the name, the transitionregion has a shape gradually changing from the circular shape of theroot region to the airfoil profile of the airfoil region. Typically, thewidth of the blade in the transition region increases substantiallylinearly with increasing distance from the hub.

As for instance blades for wind turbines have become bigger and biggerin the course of time, and they may now be more than 60 meters long, thedemand for optimised aerodynamic performance has increased. The windturbine blades are designed to have an operational lifetime of at least20 years. Therefore, even small changes to the overall performance ofthe blade may over the lifetime of a wind turbine blade accumulate to ahigh increase in financial gains, which surpasses the additionalmanufacturing costs relating to such changes. For many years, the focusareas for research have been directed towards improving the airfoilregion of the blade, but during the recent few years, more and morefocus has been directed towards also improving the aerodynamicperformance of the root and transition regions of the blade.

WO2007/065434 discloses a blade wherein the root region is provided withindentations and/or projections in order to decrease the drag from thispart of the blade.

WO2007/045244 discloses a blade, wherein the root region and thetransition region are designed so as to have at least two separateairfoil profiles in order to increase the lift of these regions.

WO0208600 describes a wind turbine, where the output of the wind turbineis increased by providing the root section of a wind turbine with amember that is designed in such a way that the assembly consisting ofthe member and the root section can absorb wind energy and increases theoverall efficiency of the wind turbine.

WO2007/118581 discloses a blade, where the inboard part of the blade isprovided with a flow guiding device on the pressure side of the blade inorder to increase the aerodynamic performance of the blade by increasingthe lift. However, the design proposed is very rigid due to thetriangular shaped cross-section and consequently the flow guiding devicehas a tendency to separate from the surface of the blade, when the bladebends.

WO2011/042527 discloses a wind turbine blade provided with a pluralityof flow guiding device parts attached to the pressure side of the blade.The longitudinally extending flow guiding parts are grouped together toform a first flow guiding device group in the transition region of theblade. The modular construction of the flow guiding device makes theconstruction more flexible and reduces peel forces at the ends of theflow guiding device parts. However, the flow guiding device parts aredesigned with a base part and a protruding plate-shaped element, andloads are still to a large degree transferred to the plate-shapedelement, when the blade bends.

Further, state of the art methods of attaching devices to the surface ofa wind turbine blade are tedious and complicated. The previous surfaceattachment techniques have required grinding of gelcoat to reveal fibrematerial for bonding, applying of adhesive, positioning of the device,removal of excess adhesive, and finally post-treatment, such aspainting, for surface visual purposes, thus involving a large number ofsteps and tools for carrying out the method.

SUMMARY OF THE INVENTION

It is an object of the invention to obtain a new blade and method ofattaching devices to the surface of a wind turbine blade, and whichovercome or ameliorate at least one of the disadvantages of the priorart or which provide a useful alternative.

According to a first aspect, the invention provides a wind turbine bladefor a rotor of a wind turbine having a substantially horizontal rotorshaft, said rotor comprising a hub, from which the wind turbine bladeextends substantially in a radial direction when mounted to the hub, thewind turbine blade having a longitudinal direction with a tip end and aroot end and a transverse direction. The wind turbine blade furthercomprises: a profiled contour including a pressure side and a suctionside, as well as a leading edge and a trailing edge with a chord havinga chord length extending there between, the profiled contour, when beingimpacted by an incident airflow, generating a lift, wherein a surfacemounted device is attached to a surface of the wind turbine blade,wherein the surface mounted device is attached to the surface of thewind turbine blade via at least a first attachment part, which isconnected to a part of the surface mounted device. The attachment partcomprises a flexible housing that forms a cavity between at least thehousing and the surface of the wind turbine blade, and the cavity isfilled with an adhesive that provides an adhesive bonding to the surfaceof the wind turbine blade.

Equivalently, the first aspect of the invention provides a flow guidingdevice, which is adapted to be attached to the surface of a wind turbineblade, via at least a first attachment part, wherein the attachment partcomprises a flexible housing that is adapted to form a cavity between atleast the housing and the surface of the wind turbine blade, the cavitybeing adapted to be filled with an adhesive that provides an adhesivebonding to the surface of the wind turbine blade.

This provides a particular advantageous embodiment with a relativediscrete or soft attachment to the surface of the blade, such that loadsfrom the blade, e.g. from bending of the blade or ovalisation of theblade shell, do not transfer up into the surface mounted device itself.Thus, the attachment at discrete parts of the surface mounted deviceprovides an embodiment, which is less likely to be damaged or detachedfrom the surface of the blade. Further, the attachment part with a gluecavity also provides a particular simple method of attaching the surfacemounted device to the surface of the blade. Since the housing of theattachment part is flexible, the attachment part may accommodate to thecurvature of the blade surface, e.g. by applying pressure to theattachment part. Thereby, the attachment provides a simple method offitting the add-ons to the surface of the blade without the need offixtures and lengthy preparation of the surface of blade. Accordingly, aworker may more quickly attach the surface mounted device to the surfaceof the blade.

The adhesive is preferably a hardened or cured adhesive.

It is clear that the surface mounted device is preferably attached to anexternal surface of the wind turbine blade. However, it may also be aninternal surface of the wind turbine blade.

The housing of the attachment part is seen to form a glue shaper or glueshoe, which may be used for attaching add-ons to the surface of theblade. The housing or attachment part may be provided with glue spacers,e.g. formed as protrusions extending from the roof of the cavity inorder to ensure a controlled thickness of the adhesive bond.

The glue cavity may be formed between the flexible housing, the surfaceof the wind turbine blade and a part of the surface mounted device. Itmay also be provided as a separate socket for screw mounting the surfacemounted device to the surface of the blade.

The attachment part is preferably connected to a proximal part of thesurface mounted device. The proximal part of the surface mounted deviceis the part, which is located nearest the blade surface and so to speakis attached to the surface of the blade. However, by utilising theattachment parts, it is clear that there may be a spacing between theproximal part of the surface mounted device and the surface of theblade.

The adhesive may for instance be PU-based, epoxy-based or MMA.

It is clear that the surface mounted device also comprises a distalpart, which is the part farthest from the surface the blade andattachment part.

According to a second aspect, the invention also provides: a windturbine blade for a rotor of a wind turbine having a substantiallyhorizontal rotor shaft, said rotor comprising a hub, from which the windturbine blade extends substantially in a radial direction when mountedto the hub, the wind turbine blade having a longitudinal direction witha tip end and a root end and a transverse direction, the wind turbineblade further comprising: a profiled contour including a pressure sideand a suction side, as well as a leading edge and a trailing edge with achord having a chord length extending there between, the profiledcontour, when being impacted by an incident airflow, generating a lift,wherein a surface mounted device is attached to a surface of the windturbine blade, characterised in that the surface mounted device isattached to the surface of the wind turbine blade via three attachmentparts, which are connected to parts of the surface mounted device andwhich attach the surface mounted device to three discrete areas on thesurface of the blade, wherein the three discrete areas when seen in atop view are arranged in a triangle.

Equivalently, the second aspect provides a flow guiding device, which isadapted to be attached to the surface of a wind turbine blade, via threeattachment parts, which are connected to parts of the surface mounteddevice and which are adapted to attach the surface mounted device tothree discrete areas on the surface of the blade, wherein the threeattachment parts when seen in a top view are arranged in a triangle.

This provides a particularly simple way of attaching add-ons to thesurface of a wind turbine blade, since the three-point attachment willalways be able to contact the surface of the blade despite having acomplex curvature, as compared to for instance a device having fourattachment parts, three attachment parts in line or a large bondingsurface along the entire extent of the device, where it may be difficultto let all (or the entirety of the) attachment parts contact the blade.Thereby, the attachment provides a simple method of fitting the add-onsto the surface of the blade without the need of fixtures and lengthypreparation of the surface of blade. Accordingly, a worker may morequickly attach the surface mounted device to the surface of the blade.

According to a third aspect, the invention also provides a wind turbineblade for a rotor of a wind turbine having a substantially horizontalrotor shaft, said rotor comprising a hub, from which the wind turbineblade extends substantially in a radial direction when mounted to thehub, the wind turbine blade having a longitudinal direction with a tipend and a root end and a transverse direction, the wind turbine bladefurther comprising: a profiled contour including a pressure side and asuction side, as well as a leading edge and a trailing edge with a chordhaving a chord length extending there between, the profiled contour,when being impacted by an incident airflow, generating a lift, wherein asurface mounted device is attached to a surface of the wind turbineblade, wherein the surface mounted device in a lengthwise direction iscurved, characterised in that a lengthwise radius of curvature of thesurface mounted device varies from a proximal part of the surfacemounted device to a distal part of the surface mounted device.

Equivalently, the third aspect of the invention provides a flow guidingdevice, which is adapted to be attached to the surface of a wind turbineblade, wherein the flow guiding device is curved in a lengthwisedirection of the device, and wherein a lengthwise radius of curvature ofthe device varies from a proximal part of the device to a distal part ofthe device.

By varying the radius of curvature of the surface mounted device, it ispossible to vary the stiffness of the device from the proximal part tothe distal part of the device and/or to better control the transfer ofloads from the blade and to the device itself.

The first, second and third aspect may be combined in any way. In thefollowing a number of embodiments is described, which are applicable toall three aspects and in particular embodiments combining all threeaspects.

According to an advantageous embodiment, the flexible housing is made ofa first material and the surface mounted device made of a secondmaterial, wherein a hardness of the first material is smaller than thehardness of the second material. Alternatively, the first material issofter than the second material. In general, the housing should be moreflexible than the surface mounted device.

The flexible housing may for instance be made of an elastomer material.Further, the housing is preferably relatively thin-walled.

According to an advantageous embodiment, the attachment part is taperedfrom a proximal part to a distal part of the attachment part, e.g. beingbell-shaped, conical shaped, or frusto-conical shaped. Accordingly, theattachment part is shaped so that it has a larger surface area at a partproximal to the surface of the blade than a part distal to the part ofthe blade, whereby the attachment part prevents a notch effect at thesurface of the blade and instead provides a gradual transition of loadstransferred from the blade and onto the surface mounted device.Preferably, the attachment part is also tapered seen in a side view sothat the height of the attachment part goes towards zero and provides aminimal notch effect.

The attachment part is advantageously formed so that a top view crosssection of the attachment device is substantially circular. According toanother advantageous embodiment, the attachment part is substantiallyoval.

Accordingly, the attachment device may be shaped similar to a flexiblesuction cup, which accommodates the surface of the blade. The cavityformed between the cup and the surface of the blade is filled with anadhesive, which is hardened or cured.

The housing of the attachment part may advantageously be made fromrubber or polyurethane, or another suitable polymer material.

In another advantageous embodiment, the attachment part is connected tothe surface mounted device via an adhesive bond or by being moulded ontothe surface mounted device. Accordingly, the attachment part may beglued onto the surface mounted device. It is also possible to mould theattachment part onto the surface mounted device via for instanceinjection moulding.

The surface mounted device or the attachment part may also be providedwith a grip or the like, which may facilitate easier handling for aworker attaching the surface mounted device to the surface of the bladeby allowing the worker to more easily press the flexible housing againstthe surface of the blade. This is particular advantageous, if the deviceis mounted on site in the field.

The surface mounted device may in an advantageous embodiment be madefrom a polymer material, such as a polyurethane, optionally reinforcedwith reinforcement fibres, such as glass fibres or carbon fibres.

In a particular advantageous embodiment, the surface mounted device ismade of a polyurethane (PUR) material, optionally reinforced withreinforcement fibres, and the attachment part is also made of apolyurethane (PUR) material. Accordingly, it is ensured that theattachment part and the device are compatible and provide a strongconnection. The two parts may be integrally formed, or the parts may befor instance injection moulded in two steps. By using PUR material, itis further fairly simple to vary the hardness and stiffness of theparts, whereby the attachment part can be made relatively flexible andthe surface mounted device may be made stiffer. A similar effect may beachieved by manufacturing the attachment device and/or surface mounteddevice in a thermoplastic material, which is particular relevant forhigh volume manufacturing. According to a preferred embodiment, thesurface mounted device is not fibre reinforced. Thus, the device may bemade of e.g. PUR or another polymer material only, which provides adevice, which is simpler and cheaper to manufacture.

In an advantageous embodiment, the attachment part comprises acircumferential lip for attaching to the surface of the wind turbineblade. The circumferential lip thus forms the lower or proximal part ofthe attachment device and glue cavity formed between the housing and thesurface of the wind turbine blade.

The circumferential lip may have a substantially flat attachment surfacefor mounting to the blade. Alternatively, the circumferential lip mayhave an inclined attachment surface so that the attachment surfaceaccommodates to the surface of the wind turbine blade, when it ispressed against said surface of the wind turbine blade.

The circumferential lip may be provided with an adhesive, such as anadhesive tape, e.g. a pressure-sensitive double-adhesive tape, forproviding a preliminary attachment to the blade surface. Thus, theadhesive provides a sealing to the blade surface, and provides the gluecavity, which is then filled with an adhesive and hardened or cured. Thetape may be provided with a liner, which is removed after the flexiblehousing has preliminary been fitted to the surface of the blade. Inanother embodiment, a preliminary attachment is provided by screwing orriveting the attachment part on to the surface of the blade as afixation during the adhesion filling process.

According to a preferred embodiment, the surface mounted device is aflow guiding device, such as a spoiler device or a Gurney flap. Thereby,it is seen that the device is a device, which changes the aerodynamicsof a part of the wind turbine blade. However, the device may also be atrailing edge element, such as a plate comprising a serrated trailingedge.

According to another preferred embodiment, the surface mounted devicecomprises a plate-shaped element, which protrudes from the surface ofthe wind turbine blade. In the following, when referring to the surfacemounted device, this may as such be a reference to the plate-shapedelement of the surface mounted device.

The surface mounted device may be oriented so that it extendssubstantially in the longitudinal direction of the blade, i.e. thelengthwise direction of the surface mounted device is orientedsubstantially in the longitudinal direction of the blade. By“substantially in the longitudinal direction” is meant that thelengthwise direction of the surface mounted device forms an angle of 30degrees or less to the longitudinal direction of the blade,advantageously 20 degrees or less, and even more advantageously 10degrees or less.

According to another preferred embodiment, the surface mounted device isarranged on the pressure side of the blade. The surface mounted device,e.g. a flow-guiding device, may for instance be positioned at thetrailing edge and forming a Gurney flap. However, according to apreferred embodiment, the surface mounted device is a spoiler device,which is arranged in a distance from the trailing edge of the blade,e.g. in a position between a position of maximum thickness of the bladeprofile and the trailing edge of the blade. Accordingly, the surfacemounted device may be arranged so as to generate a separation of airflowfrom the pressure side of the blade at a point between the surfacemounted device and the trailing edge of the blade, when the blade isimpacted by the incident airflow. Accordingly, the surface mounteddevice or flow guiding device facilitates a pressure build-up betweenthe device and the trailing edge and thus increased lift.

In one advantageous embodiment, the surface mounted device is curved ina lengthwise direction of the device. Such a design has the advantagethat the surface mounted device may be stretched slightly in thelengthwise direction, e.g. when the blade bends or the blade shellovalises. It is clear that it is the plate-shaped element that may becurved in the lengthwise direction.

In a particular advantageous embodiment, a lengthwise radius ofcurvature of the surface mounted device varies from a proximal part ofthe surface mounted device to a distal part of the surface mounteddevice. The radius of curvature may for instance increase from theproximal part to the distal part of the surface mounted device. Thisprovides a simple embodiment, where the distal part of the device may bemade stiffer than the proximal part. Accordingly, the proximal part maybetter accommodate to blade bending, whereas the distal part may betterwithstand the wind pressure and facilitate a build-up of pressure. Thecurvature of radius of the distal part may for instance approachinfinity, in which case the distal part of the device is straight. In analternative embodiment, the radius of curvature decreases from theproximal part to the distal part of the surface mounted device. Thesurface mounted device may for instance be formed as a part of afrusto-conical shape.

In one particularly advantageous embodiment, the surface mounted deviceis reinforced with a grid or rib structure. The grid or rib structuremay for instance be provided as surface protrusions. The ribs may forinstance be arranged along the two end parts of the plate-shapedelement, and with a rib extending along a distal part of theplate-shaped element. Further or alternatively, the plate-shaped elementmay be provided with cross-ribs extending from near a distal part andend part and to a proximal and intermediate part of the plate-shapedelement. This provides a strong triangular rib structure that addsstrength to the plate shaped element. The rib or grid design may readilybe moulded together with the plate-shaped element, in particular if theplate-shaped element is formed in PUR.

The plate-shaped element is advantageously not provided with a rib alongthe proximal part of the plate-shaped element, since this would preventthe plate-shaped element to accommodate blade bending or ovalisation.Thereby, the blade surface as such provides the third side (withvariable length) of a triangle that provides stiffness to theplate-shaped element.

Overall, it is seen that the invention according to a fourth aspectprovides a flow guiding device that comprises a plate-shaped element,which is reinforced with a rib structure, e.g. according to any of theprevious embodiments. This provides the possibility of manufacturing theplate-shaped element in a polymer material without the need to fibrereinforce the structure.

The thickness of the spoiler is advantageously 0.5-10 mm, e.g. around1-3 mm. The thickness of the rib or grid structure is advantageously5-50 mm, e.g. around 15 mm.

The longitudinal length of the surface mounted device is advantageously20-150 cm, or 25-120 cm. The height of the surface mounted device isadvantageously 3-50 cm.

The hardness of the flexible housing is advantageously 20-75 on theShore A scale, e.g. around 55 on the shore A scale. The hardness of thesurface mounted device is advantageously 45-100 on the shore D scale,e.g. around 75 on the shore D scale. The lip of the attachment deviceadvantageously has a maximum external dimension, such as an outerdiameter, of 1-15 cm, or 2-10 cm. Thus, the proximal part of theattachment device may have this maximum external dimension.

In one embodiment, the surface mounted device is connected to theattachment part such that a spacing between a proximal part of thesurface mounted device and the surface of the wind turbine blade is inthe interval 1-20 mm, e.g. around 10 mm.

The plate-shaped element may be made with a flexibility that allows theplate-shaped element to deflect at high wind speeds and thereby reduceloads to the blade.

In another embodiment, the surface mounted device may be angled towardsthe leading edge of the blade so as to provide a pocket between thesurface mounted device and the surface of the blade, said pocket facingtowards the leading edge of the blade. This provides a spoiler device,which facilitates a build-up of pressure both in front of and behind thespoiler device, thereby increasing lift even further.

The surface mounted device (or plate-shaped element) is advantageouslycurved towards the leading edge of the blade, thus also providing thepocket between the surface mounted device and the surface of the blade.With a flexible plate-shaped element, this design also allows thesurface mounted design to be collapsed or pressed against the surface ofthe blade, e.g. by use of straps, since the device will be flexible in adirection towards the leading edge of the blade and stiff in thedirection of the incoming flow. This may be advantageous for transportpurposes.

The surface mounted device may for instance be angled 5-45 degrees, or10-40 degrees, e.g. around 25 degrees, compared to a surface normal atthe attachment point. However, in principle, the surface mounted devicemay also be protruding substantially normal to a blade surface or beangled towards the trailing edge of the blade.

In an advantageous embodiment, the wind turbine blade is provided with aplurality of surface mounted devices. The plurality of surface mounteddevices may for instance be arranged as longitudinally extending flowguiding device parts, which are grouped together to form a first flowguiding device group.

The plurality of surface mounted devices may advantageously be arrangedin substantially mutual lengthwise extensions of each other.Accordingly, the flow guiding devices may be arranged juxtaposed with asmall spacing between them or so that ends of juxtaposed devicessubstantially abut each other. The flow guiding devices may also bearranged slightly overlapping in the longitudinal direction.

The flow guiding devices may be arranged with a longitudinal spacingbetween the flow guiding parts. The longitudinal spacing may e.g. lie inan interval between 5 mm and 50 mm, or between 5 mm and 40 mm, orbetween 5 mm and 30 mm, e.g. around 10 mm. In one embodiment, thespacing between adjacent flow guiding parts is closed with a flexiblebody, e.g. made of a rubber material.

Thus, the first flow guiding device group may comprise separate ormodular parts in particular in the longitudinal direction of the blade.The modular construction makes the construction more flexible andreduces peel forces at the ends of the flow guiding device parts. Thus,the modular parts have a smaller tendency to break off from the surfaceof the blade.

Longitudinally extending means that the flow guiding device parts areextending substantially in the longitudinal direction of the blade.Thus, the device parts typically have a first side (nearest the leadingedge) and a second side (nearest the trailing edge) as well as a firstlongitudinal end (nearest the root end) and a second longitudinal end(nearest the tip end).

Advantageously, the first side faces substantially towards the leadingedge of the blade.

The flow guiding device is preferably permanently attached to thesurface of the wind turbine blade and cannot be actively controlled.Thus, the orientation of the front surface is non-adjustable. Also, itis recognised that the flow guiding device is utilised for increasingthe lift and the energy yield. Thus, the flow guiding device mayalternatively be denoted as a high lift device.

By incident flow is meant the inflow conditions at a blade sectionduring normal use of the blade, i.e. rotation on a wind turbine rotor.Thus, the incoming flow is the inflow formed by the resultant of theaxial wind speed and the rotational component as it is seen by the localsection of the blade. By oncoming flow is meant the flow impinging theflow guiding device, i.e. the local flow on the pressure side of theblade meeting and impacting the flow guiding device.

According to one embodiment, the flow guiding device parts are spoilerdevice parts. Again, it must be pointed out that the parts arepreferably non-adjustable and arranged to increase the lift of the windturbine blade and thus the energy yield of the wind turbine.Accordingly, the spoiler parts are not used for breaking purposes.

According to an advantageous embodiment, the flow guiding device partscomprise planar or plate-shaped elements protruding from the profile.Thereby, a particularly simple design of the flow guiding device partsis provided. Furthermore, this design is much more flexible than thetypically wedge-shaped design, which is very rigid. Thus, the planardesign has a smaller tendency to have high joint loads, which in worstcase can make the flow guiding device parts break off from the surfaceof the wind turbine blade.

According to an advantageous embodiment, the flow guiding device partstogether form a substantially continuous first side facing towards theleading edge of the blade so that the flow guiding device parts togetherform a flow guiding device, which is arranged and adapted to form aseparated airflow between the glow guiding device and the trailing edgeof the blade.

According to one advantageous embodiment, the flow guiding device partsare shaped so that they have an inflow surface with a start pointoriented towards the leading edge of the blade and an end point orientedtowards the trailing edge of the blade, the distance between the inflowsurface and the profiled contour increasing from the start point to theend point. Thus, the flow guiding device parts may have a substantiallywedge shaped or triangularly shaped profile. However, the inflow surfacemay also be provided by a planar element oriented backwardly or towardsthe trailing edge of the blade. The angle of the inflow surface andsurface height of a distal point of the inflow surface mayadvantageously correspond to those described in European patentapplications WO2010066500 and WO2010066501, respectively, by the presentapplicant.

According to an advantageous embodiment, the flow guiding device of theblade has a front surface facing towards the oncoming airflow and havinga proximal point located at the profiled contour and a distal pointlocated at a distance (i.e. with a spacing) from the profiled contour ofthe blade, wherein the profiled contour has a surface normal at theproximal point, and wherein the front surface of the flow guiding devicecomprises at least a first portion, which is angled towards an oncomingairflow so that an average tangent or median line to said first portionforms a first angle with the surface normal being larger than 0 degrees.

Accordingly, the front surface of the flow guiding device, seen from theproximal point, is angled towards the oncoming airflow and thus alsotowards the leading edge of the blade. Thus, when the profiled contourof the blade is impacted by the incident airflow, the flow guidingdevice creates an air pocket in front of the front surface, whichincreases the local pressure in front of the flow guiding device, andwhich guides the airflow around the flow guiding device. Further, theflow guiding device functions as an obstruction to the flow on thepressure side of the profile. Downstream of the flow guiding device,i.e. typically between the flow guiding device and the trailing edge ofthe blade, a separation of the airflow occurs. This obstruction isresulting in a higher pressure after the flow guiding device, i.e.between the flow guiding device and the trailing edge of the windturbine blade, due to a detachment of the flow. Thus, the pressure isincreased both in front and behind of the flow guiding device, which inturn increases the lift significantly on this section of the blade atthe governing inflow angles for this section. A realistic estimate ofthe potential performance improvement is 1-2% of annual energy yieldcompared to conventional wind turbine blades without such flow guidingdevices.

The terms average tangent or median line here mean that the firstportion of the front surface on average is angled towards the oncomingflow. This corresponds to a linear fit to the first portion of the frontsurface of the flow guiding device being angled towards the oncomingflow and the leading edge of the blade.

The forwardly angled first portion also results in a tangent to theprofile and the tangent or median line to the first portion of the frontsurface forming an angle being less than 90 degrees.

From the definitions, it is clear that the front surface may comprise asecond portion, which is not angled towards the oncoming flow and theleading edge of the blade.

According to an advantageous embodiment, the first angle is at least 5degrees, or at least 10 degrees, or at least 15 degrees. The first anglemay even be at least 20 degrees or at least 25 degrees or at least 30degrees. Higher angles more efficiently provide the air pocket and mayalso decrease the drag, since the front surface does not have toprotrude as much from the surface in order to provide the build-up ofpressure in front of the flow guiding device. On the other hand evenhigher angles make the effective height of the flow guiding devicesmaller.

According to another advantageous embodiment, the front surface isconcave. The front surface of the flow guiding device may guide theairflow across the concave surface and thus contribute further toforming a re-circulating zone in front of the flow guiding device.

According to yet another advantageous embodiment, the plurality oflongitudinally extending flow guiding device parts comprises individualflow guiding device parts, which are at least partially overlapping inthe longitudinal direction of the blade. Thus, the individual flowguiding device parts are individually displaced in the transversedirection of the blade. Accordingly, a first end of a first flow guidingdevice extends beyond the radial position of a second end of a secondflow guiding device part.

In one embodiment, the individual flow guiding device parts aresubstantially straight in the longitudinal direction. In anotherembodiment, the individual flow guiding device parts are curved in thelongitudinal direction. For example, every second flow guiding devicepart may be convex and the others concave. This can also be combinedwith the partially overlapping design.

According to yet another advantageous embodiment, the first flow guidingdevice group has a corrugated design in the longitudinal direction,advantageously at least a distal point of a plate-shaped element. Thedesign may for instance be wavy in the longitudinal direction andcomprise alternating flow guiding device parts being concave and convex,respectively. Alternatively, a trapezium shaped design may be used.These designs have the advantage that the flow guiding device parts maybe stretched slightly in the longitudinal direction, when the bladebends. The individual flow guiding device parts may also be corrugated.

Preferably, the flow guiding device group is formed as a longitudinallyextending device. According to an advantageous embodiment, the flowguiding device group extends along at least 5% of a longitudinal extentof the wind turbine blade. Yet again, the longitudinal extent of theflow guiding device group may be at least 7%, 10%, 15%, or even 20% ofthe longitudinal extent or length of the blade.

According to another embodiment, the longitudinally extending flowguiding device group extends along at least 1 meter of the blade, or atleast 2 meters, or at least 3 meters, or at least 4 meters, or at least5 meters, or at least 6 meters, or even at least 8 or 10 meters of thewind turbine blade.

The wind turbine blade or at least an aerodynamic shell of the windturbine may advantageously be made of a composite structure, such as apolymer matrix reinforced with a fibre reinforcement material, such asglass fibres or carbon fibres. The resin may be a thermosetting resin,such as epoxy, vinylester, polyester. The resin may also be athermoplastic, such as nylon, PVC, ABS, polypropylene or polyethylene.Yet again the resin may be a thermosetting thermoplastic, such as cyclicPBT or PET. The flow guiding device may also be made of such compositematerials. The polymer matrix material may also be a polyurethane resin.

The wind turbine blade may be made with a load bearing spar beam and anaerodynamic shell attached to said beam. Alternatively, the load bearingstructure may be integrated into the blade shell with spar caps (alsocalled main laminates) integrated in the blade shell and intermediateshear webs attached between the spar caps.

In one embodiment, the profiled contour is divided into a root regionhaving a substantially circular or elliptical profile closest to thehub, an airfoil region having a lift-generating profile furthest awayfrom the hub, and a transition region between the root region and theairfoil region, the transition region having a profile graduallychanging in the radial direction from the circular or elliptical profileof the root region to the lift-generating profile of the airfoil region.The surface mounted device may advantageously be provided in thetransition region of the blade.

According to a particular advantageous embodiment, the flow guidingdevice is arranged in the transition region of the profiled contour,preferably on the pressure side of the blade. The device can increasethe lift in the transition region and thus contribute to the energyyield. Advantageously, the flow guiding device extends substantiallyalong an entire longitudinal extent of the transition region, thuscontributing to the increased lift along the entire transition region.

Yet again, the flow guiding device may advantageously extend into theairfoil region. This will add lift to the airfoil region and thusincrease the annual energy yield. In principle it may also extend intothe root region. Also, the flow guiding device may be arranged in theroot region alone, or in the airfoil region alone.

In a preferred embodiment, the surface mounted device is attached to thesurface of the blade via three attachment parts, wherein a firstattachment part is connected near a first end of the surface mounteddevice, a second attachment part is connected near a second end of thesurface mounted device, and a third attachment part is connected at anintermediate part of the surface mounted device. The three attachmentparts may, when seen in a top view, be arranged in a triangle on thesurface of the wind turbine blade. The triangle may have an acute anglebeing at least 5 degrees, or at least 10 degrees.

In one advantageous embodiment, the attachment part or the flexiblehousing is made of a double-adhesive tape. This provides a particularsimple method of forming the shape of the attachment part and the cavitywhich is to be filled with the adhesive, which forms the adhesivebonding.

Accordingly, the double-adhesive tape may in one embodiment form acircumferential part between the surface of the wind turbine blade andthe surface mounted device, and further form a cavity between thedouble-adhesive tape, the surface of the wind turbine blade and a partof the surface mounted device.

In one advantageous embodiment, the double-adhesive tape comprises alayer of compressible material. This provides a viscoelastic housing.The compressible material may for instance be a layer of foam cells,such as acrylic foam. The double-adhesive tape may have a thickness ofat least 0.5 mm, and preferably at least 1 mm. Further, the adhesivetape may have a thickness of maximum 10 mm, or maximum 7 mm, or maximum5 mm. Accordingly, a cavity having a height of 0.5 mm to 10 mm may beformed, e.g. having a height of 1 mm to 5 mm.

According to another aspect, the invention provides a wind turbinecomprising a number of blades, preferably two or three, according to anyof the aforementioned embodiments.

The first aspect of the invention also provides a method of attaching asurface mounted device to a surface of a wind turbine blade, wherein thewind turbine blade has a longitudinal direction with a tip end and aroot end and a transverse direction, wherein the wind turbine bladefurther comprises a profiled contour including a pressure side and asuction side, as well as a leading edge and a trailing edge with a chordhaving a chord length extending there between, the profiled contour,when being impacted by an incident airflow, generating a lift, whereinthe method comprises the steps of:

-   -   a) providing the wind turbine blade,    -   b) proving a surface mounted device for mounting on the surface        of the blade, the surface mounted device having at least one        attachment part connected to a part of the surface mounted        device, wherein the attachment part comprises a flexible housing        adapted to form a cavity between at least the housing and the        surface of the wind turbine blade,    -   c) positioning the attachment part on a first discrete area of        the surface of the blade so that a cavity is formed between at        least the housing and the surface of the wind turbine blade,    -   d) injecting an adhesive or resin into the cavity, and    -   e) curing or hardening the adhesive or resin so that the device        is attached to the surface of the wind turbine blade via an        adhesive bonding.

The method involving an attachment part with a glue cavity also providesa particular simple method of attaching the surface mounted device tothe surface of the blade.

Since the housing of the attachment part is flexible, the attachmentpart accommodates to the curvature of the blade surface, e.g. byapplying pressure to the attachment part. The exact position of thedevice may also be fine-tuned by carefully moving the attachment partsso that the desired position is obtained. Overall, the new attachmentmethod provides a simple method of fitting the add-ons to the surface ofthe blade without the need of fixtures and lengthy preparation of thesurface of blade. Further, the flexible housing also acts as a glueshaper and glue stopper, which alleviates the subsequent need forfinishing operations, such as removal of excessive adhesive.Accordingly, a worker may more quickly attach the surface mounted deviceto the surface of the blade than with prior art techniques.

The cavity may be formed by pressing the attachment part against thesurface of the blade.

The attachment part is preferably previously connected to the device,e.g. by gluing or moulding the attachment part onto the device. Theconnection part is preferably connected to a proximal part of thesurface mounted device. The proximal part of the surface mounted deviceis the part, which is located nearest the blade surface and so to speakis attached to the surface of the blade. However, by utilising theattachment parts, it is clear that there may be a spacing between theproximal part of the surface mounted device and the surface of theblade. However, in principle, the attachment device may in analternative embodiment be connected to the device as part of the gluefilling and hardening steps of steps d) and e).

It is clear that the surface mounted device is preferably attached to anexternal surface of the wind turbine blade. However, it may also be aninternal surface of the wind turbine blade.

In one embodiment, the first discrete area of the wind turbine blade isdegreased prior to step a, e.g. via an alcohol based rub. Thereby, it isensured that an effective adhesive bond can be provided to the surfaceof the blade. The degreasing is advantageously carried out on a gelcoatof the wind turbine blade. However, compared to previous attachmentmethods, it is not necessary to grind the gelcoat in order to revealfibre material for bonding.

In a preferred embodiment, the attachment part comprises acircumferential lip for attaching to the surface of the wind turbineblade. The circumferential lip thus forms the lower or proximal part ofthe attachment device and seals to the surface of the blade, therebyforming the glue cavity between the housing and the surface of the windturbine blade. The circumferential lip may have a substantially flatattachment surface for mounting to the blade. The circumferential lipmay alternatively have an inclined attachment surface so that theattachment surface accommodates to the surface of the wind turbineblade, when it is pressed against said surface of the wind turbineblade.

The circumferential lip may be provided with an adhesive, such as anadhesive tape, e.g. a pressure-sensitive double-adhesive tape, forproviding a preliminary attachment to the blade surface. This isparticular useful of in situ retrofitting of add-ons to the surface ofthe blade.

Thus, the tape provides a sealing to the blade surface, and provides theglue cavity, which is then filled with an adhesive and hardened orcured. The preliminary attachment may ensure that the attachment partdoes not move during the injection step, and further prevents thatadhesive escapes from the sides of the attachment device during theinjection step. This is particular advantageous, since the injection ofadhesive may be carried out without previous evacuation of the cavity,and in that the injection of adhesive may build up pressure in thecavity.

The tape may be provided with a liner. The liner is advantageouslyprovided with a tap so that the liner can be pulled out from the lip.Thus, the lip of the attachment part may be pressed against the surfaceof the blade. Once the device and attachment part are located in thecorrect position, the liner is removed, whereby the lip is preliminaryattached to the surface of the wind turbine blade, and after whichinjection of adhesive into the cavity may be carried out.

In an alternative embodiment, a few drops of adhesive are applied to thelip of the flexible housing. The fastening element can still be movedalong the blade surface and once the desired position is found, the lipis simply pressed against the blade surface until the adhesive at leastpartially hardens and provides a preliminary attachment to the bladesurface.

In another embodiment, the attachment part is prior to step d)mechanically fixed to the surface of the wind turbine blade, e.g. via ascrew connected through the attachment part and to an alignment holeformed in the surface of the wind turbine blade. The mechanical fixationmeans, e.g. the screw, may be removed after the injection and curing ofadhesive. The hole from the screw may then be filled with a sealant.

In another embodiment, a micro-environment treatment is carried out inthe cavity prior to step d). The micro-environment treatment may forinstance be chosen from the group of evacuating the cavity, heating thecavity, or a degasification, e.g. via filling the cavity with nitrogen.Thereby, the cavity may be dried before the injection step, which mayimprove the adhesive bond even further, since moist is removed prior tothe injection.

It is also possible to position the attachment part on the blade of thesurface by use of a fixture to keep the attachment part in place, whilethe adhesive is injected into the cavity. This embodiment is particularuseful, if the add-ons are mounted to the surface of the blade at thefactory.

In one advantageous embodiment, the flexible housing is provided with abore from the cavity to an exterior. Thereby, gas or air is able toescape from the cavity during the injection step. The bore is preferablyrelatively small. The bore may advantageously be provided near a distalpart of the flexible housing, whereby the adhesive or resin filled intothe cavity pushes the air towards a top part of the cavity. It is alsopossible to apply suction to the bore. The bore may also provide avisual confirmation of the filling process, e.g. when liquid adhesivestarts pouring out from the hole, the injection of the adhesive may bestopped.

The flexible housing may also be made of an at least partiallytransparent material, such that the filling process can easily bemonitored.

The cavity may be connected to an adhesive reservoir or chamber duringthe curing or hardening in step e). Thus, if the adhesive shrinks duringthe hardening, additional liquid adhesive will be drawn into the cavityand fill the voids. The adhesive of the reservoir should of courseharden at a later stage than the adhesive in the cavity such that liquidadhesive is not drawn in the wrong direction.

In a first additional aspect of the invention, the attachment part orthe flexible housing of the attachment part is made from double-adhesivetape, wherein the double-adhesive tape is arranged to form acircumferential part and so as to form a cavity formed by partly by thedouble-adhesive tape, the surface of the blade, and a part of thesurface mounted device.

In other words, the first additional aspect provides a wind turbineblade for a rotor of a wind turbine having a substantially horizontalrotor shaft, said rotor comprising a hub, from which the wind turbineblade extends substantially in a radial direction when mounted to thehub, the wind turbine blade having a longitudinal direction with a tipend and a root end and a transverse direction, the wind turbine bladefurther comprising:

-   -   a profiled contour including a pressure side and a suction side,        as well as a leading edge and a trailing edge with a chord        having a chord length extending there between, the profiled        contour, when being impacted by an incident airflow, generating        a lift, wherein    -   a surface mounted device is attached to a surface of the wind        turbine blade, wherein    -   the surface mounted device is attached to the surface of the        wind turbine blade via at least a first attachment part, which        is connected to a part of the surface mounted device, wherein    -   the attachment part comprises a flexible housing made of an        double-adhesive tape that forms a cavity between at least the        housing, the surface of the wind turbine blade, and a part of        the surface mounted device, and wherein    -   the cavity is filled with an adhesive that provides an adhesive        bonding to the surface of the wind turbine blade.

Similar to the previous embodiments, the double-adhesive tape may form acircumferential part, such as a lip, of the flexible housing.

The circumferential part may have a small opening, such that it mayprovide a visual confirmation of the filling process, e.g. when liquidadhesive starts pouring out from the hole, the injection of the adhesivemay be stopped.

In one advantageous embodiment, the double-adhesive tape comprises alayer of compressible material. This provides viscoelastic housing. Thecompressible material may for instance be a layer of foam cells, such asacrylic foam. The double-adhesive tape may have a thickness of at least0.5 mm, and preferably at least 1 mm. Further, the adhesive tape mayhave a thickness of maximum 10 mm, or maximum 7 mm, or maximum 5 mm.Accordingly, a cavity having a height of 0.5 mm to 10 mm may be formed,e.g. having a height of 1 mm to 5 mm.

In a second additional aspect, the invention provides a method ofattaching a surface mounted device to a surface of a wind turbine blade,wherein the wind turbine blade has a longitudinal direction with a tipend and a root end and a transverse direction, wherein the wind turbineblade further comprises a profiled contour including a pressure side anda suction side, as well as a leading edge and a trailing edge with achord having a chord length extending there between, the profiledcontour, when being impacted by an incident airflow, generating a lift,wherein the method comprises the steps of:

-   -   a) providing the wind turbine blade,    -   b) arranging double-adhesive tape on the surface of the wind        turbine blade so as to form a circumferential part of an        attachment part    -   c) arranging a device for mounting on the surface of the blade        on the double-adhesive tape so that a cavity of an attachment        part is formed between at least the double-adhesive tape, the        surface of the wind turbine blade, and a part of the device,    -   d) injecting an adhesive or resin into the cavity, and    -   e) curing or hardening the adhesive or resin so that the device        is attached to the surface of the wind turbine blade via an        adhesive bonding.

It is recognised that the double-adhesive tape may be arranged directlyon the surface of the wind turbine blade and that the device is thenlater arranged on top of the double-adhesive tape in order to form thecavity, or alternatively that the double-adhesive tape may be arrangedon the device and that the device with the double-adhesive tape is thenarranged on the surface of the wind turbine blade in order to form thecavity.

BRIEF DESCRIPTION OF THE FIGURES

The invention is explained in detail below with reference to embodimentsshown in the drawings, in which

FIG. 1 shows a wind turbine,

FIG. 2 shows a schematic view of a first embodiment of a wind turbineblade provided with flow guiding device parts according to theinvention, seen in perspective,

FIG. 3 shows a schematic view of an airfoil profile,

FIG. 4 shows a top view of a wind turbine blade according to theinvention,

FIG. 5 shows various views of a flow guiding device according to theinvention and provided with attachment parts according to the invention,

FIG. 6 shows two embodiments of a proximal part of a flow guiding deviceaccording to the invention with an attachment part according to theinvention,

FIG. 7 shows cross-sectional views of two embodiments of attachmentparts according to the invention,

FIG. 8 illustrates an adhesive injection step of a method according tothe invention,

FIG. 9 shows a group of flow guiding devices,

FIG. 10 shows a first embodiment of top parts of a group of flow guidingdevices,

FIG. 11 shows a second embodiment of top parts of a group of flowguiding devices,

FIG. 12 shows a third embodiment of top parts of a group of flow guidingdevices,

FIG. 13 shows a fourth embodiment of top parts of a group of flowguiding devices,

FIG. 14 shows a fifth embodiment of top parts of a group of flow guidingdevices,

FIG. 15 shows a top view of a wind turbine blade provided with serratedtrailing edge panels,

FIG. 16 shows a top view of a serrated trailing edge panel provided withan attachment part according to the invention,

FIG. 17 shows a top view of a serrated trailing edge panel provided withthree attachment parts according to the invention,

FIG. 18 shows a top view of a first embodiment of a serrated trailingedge panel, where the attachment part is made from double-adhesive tape,

FIG. 19 shows a top view of a second embodiment of a serrated trailingedge panel, where the attachment part is made from double-adhesive tape,

FIG. 20 shows a top view of a part of a blade with an area prepared forarrangement of surface mounted devices,

FIG. 21 shows a template for drilling alignment holes in the areaprepared for arrangement of surface mounted devices,

FIG. 22 shows areas prepared for mounting of the attachment parts of thesurface mounted devices, and

FIG. 23 shows an additional embodiment of a proximal part of a flowguiding device according to the invention with an attachment partaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a conventional modern upwind wind turbine accordingto the so-called “Danish concept” with a tower 4, a nacelle 6 and arotor with a substantially horizontal rotor shaft. The rotor includes ahub 8 and three blades 10 extending radially from the hub 8, each havinga blade root 16 nearest the hub and a blade tip 14 farthest from the hub8.

FIG. 3 shows a schematic view of an airfoil profile 50 of a typicalblade of a wind turbine depicted with the various parameters, which aretypically used to define the geometrical shape of an airfoil. Theairfoil profile 50 has a pressure side 52 and a suction side 54, whichduring use—i.e. during rotation of the rotor—normally face towards thewindward side and the leeward side, respectively. The airfoil 50 has achord 60 with a chord length c extending between a leading edge 56 and atrailing edge 58 of the blade. The airfoil 50 has a thickness t, whichis defined as the distance between the pressure side 52 and the suctionside 54. The thickness t of the airfoil varies along the chord 60. Thedeviation from a symmetrical profile is given by a camber line 62, whichis a median line through the airfoil profile 50. The median line can befound by drawing inscribed circles from the leading edge 56 to thetrailing edge 58. The median line follows the centres of these inscribedcircles and the deviation or distance from the chord 60 is called thecamber f. The asymmetry can also be defined by use of parameters calledthe upper camber and lower camber, which are defined as the distancesfrom the chord 60 and the suction side 54 and pressure side 52,respectively.

FIG. 2 shows a schematic view of a first embodiment of a wind turbineblade 10 according to the invention. The wind turbine blade 10 has theshape of a conventional wind turbine blade and comprises a root region30 closest to the hub, a profiled or an airfoil region 34 farthest awayfrom the hub and a transition region 32 between the root region 30 andthe airfoil region 34. The blade 10 comprises a leading edge 18 facingthe direction of rotation of the blade 10, when the blade is mounted onthe hub, and a trailing edge 20 facing the opposite direction of theleading edge 18.

The airfoil region 34 (also called the profiled region) has an ideal oralmost ideal blade shape with respect to generating lift, whereas theroot region 30 due to structural considerations has a substantiallycircular or elliptical cross-section, which for instance makes it easierand safer to mount the blade 10 to the hub. The diameter (or the chord)of the root region 30 is typically constant along the entire root area30. The transition region 32 has a transitional profile 42 graduallychanging from the circular or elliptical shape 40 of the root region 30to the airfoil profile 50 of the airfoil region 34. The width of thetransition region 32 typically increases substantially linearly withincreasing distance r from the hub.

The airfoil region 34 has an airfoil profile 50 with a chord extendingbetween the leading edge 18 and the trailing edge 20 of the blade 10.The width of the chord decreases with increasing distance r from thehub.

The chords of different sections of the blade normally do not lie in acommon plane, since the blade may be twisted and/or curved (i.e.pre-bent), thus providing the chord plane with a correspondingly twistedand/or curved course, this being most often the case in order tocompensate for the local velocity of the blade being dependent on theradius from the hub.

The wind turbine blade 10 according to the invention is provided with anumber of surface mounted devices in form of flow guiding device parts70, which are grouped together and protrude from the pressure side ofthe blade in at least the transition region 32 of the blade so as toform a flow guiding device group 95 as shown in top view in FIG. 4.However, advantageously the flow guiding device parts 70 may also extendinto the airfoil region 34 and/or the root region 30 of the blade.

FIGS. 5a-e show a flow guiding device part 70 according to theinvention, which is adapted to function as a spoiler and attached to thesurface of a wind turbine blade, e.g. as shown in FIGS. 2 and 4. FIG. 5ashows a bottom view, FIG. 5b shows a side view, FIG. 5c shows a rearview, FIG. 5d shows a perspective view showing the rear, and FIG. 5eshows another perspective view showing the front of the flow guidingdevice part 70.

It is seen that the flow guiding device part 70 comprises a plate-shapedelement 71 that protrudes from the surface of the blade, when the flowguiding device part 70 is mounted to the surface of the blade, and whichprovides an obstruction to the incoming flow. The plate-shaped element71 comprises a front surface 72, which faces towards the leading edge 18of the blade 10 and thus towards the incoming flow, and a rear surface73, which faces towards the trailing edge 20 of the blade 10 and thusaway from the incoming flow.

The plate-shaped element 71 comprises a proximal part 74 or lower part,which—when the flow guiding device part 70 is mounted to the surface ofthe blade—is located nearest the blade surface, and a distal part 75 orupper part, which is located farthest from the blade surface. Theplate-shaped element 71 is curved in the lengthwise or longitudinaldirection and has a first curvature of radius at the proximal part 74 ofthe plate-shaped element 71 and a second curvature of radius at thedistal part 75 of the plate-shaped element.

In the shown embodiment, the plate-shaped element 70 forms part of theouter surface of a frusto-conical element and thus the second radius ofcurvature is smaller than the first curvature of radius. However, in analternative embodiment, the second curvature of radius is larger thanthe first curvature of radius, which may provide a stiffer structure tothe distal part 75 of the plate-shaped element 71. The second radius ofcurvature may for instance approach infinity, in which case the distalpart 75 of the plate-shaped element 71 is straight. In yet anotherembodiment, the radius of curvature may be constant from the proximalpart 74 to the distal part 75 of the plate-shaped element.

The plate-shaped element 71 is further angled forwards towards theleading edge of the blade so as to provide a pocket between theplate-shaped element 71 and the surface of the blade, said pocket facingtowards the leading edge of the blade. Since the plate-shaped element 71is curved towards the leading edge of the blade (i.e. being concave asseen from the leading edge of the blade), this also attributes toforming the pocket between the surface mounted device and the surface ofthe blade. With a flexible plate-shaped element 71, this design alsoallows the surface mounted design to be collapsed or pressed against thesurface of the blade, which may be advantageous for transport purposes.

The flow guiding device part 70 comprises three attachment parts 77,which are utilised to attach the flow guiding device part 70 to thesurface of the blade. Each of the attachment parts 77 are tapered from aproximal part to a distal part of the attachment part 77 such that theproximal part has a greater surface area than the distal part. Theattachment part may for instance be substantially bell-shaped, conicalor frusto-conical shaped. This minimises notch effects at the surface ofthe blades and provides a gradual transition of loads transferred fromthe blade 10 and onto the flow guiding device part 70, when the bladebends or the blade shell ovalises. As seen in FIG. 5c , the attachmentpart 77 is preferably also tapered in the side-view so that the heightof the attachment part 77 approaches zero at a circumference, thusminimising the notch effect.

The attachment part 77 further includes a flexible housing 80, whichforms a cavity between at least the flexible housing 80 and the surfaceof the wind turbine blade. A part of the attachment part 77 may bemoulded as a first piece together with the plate-shaped element 71, andthe flexible housing 80 may be moulded onto this first piece.Alternatively, the flexible housing may be glued onto and/ormechanically connected to the first piece.

The flow guiding device part 70 may be attached to three discrete areason the surface of the blade, wherein the three discrete areas when seenin a top view are arranged in a triangle as for instance seen in FIG. 5a. This provides a particularly simple way of attaching add-ons to thesurface of a wind turbine blade, since the three-point attachment willalways be able to contact the surface of the blade despite having acomplex curvature. The triangle may have an acute angle being at least 5degrees, or at least 10 degrees.

The plate-shaped element 71 may, as seen in FIGS. 5a and 5e , further bereinforced with a grid or rib structure 76. The ribs may for instance bearranged along the two end parts of the plate-shaped element 71, andwith a rib extending along a distal part of the plate-shaped element.Further or alternatively, the plate-shaped element may be provided withcross-ribs extending from near a distal part and end part and to aproximal and intermediate part of the plate-shaped element 71. Thisprovides a strong triangular rib structure that adds strength toplate-shaped element 71. The rib or grid design may readily be mouldedtogether with the plate-shaped element 71. The grid or rib structure mayfor instance be provided as surface protrusions.

The flow guiding device part 70 may further be provided with a grip orthe like, e.g. provided on the attachment part 77 as shown in FIG. 5e .This grip 78 may facilitate easier handling for a worker attaching theflow guiding device part 70, which can use the grip to better press theflexible housing against the surface of the blade. This is particularlyadvantageous, if the flow guiding device parts 70 are mounted on site.

The thickness t_(s) of the plate-shaped element 71 is advantageously0.5-10 mm, e.g.

around 1.5-3 mm. The thickness t_(r) of the rib or grid structure 76 isadvantageously 5-50 mm. The longitudinal length l of the surface mounteddevice is advantageously 20-150 cm, or 25-120 cm. The height h of thesurface mounted device is advantageously 3-50 cm. The plate-shapedelement 71 is preferably connected to the attachment part 77 such that aspacing s between the proximal part 74 of the plate-shaped element 71and the surface of the wind turbine blade is in the interval 1-20 mm,e.g. around 10 mm.

The flow guiding device 70 and the attachment part 77 may be made ofpolyurethane (PUR) material or a thermoplastic polymer, optionallyreinforced with reinforcement fibres, and the attachment part is alsomade of a polyurethane (PUR) or thermoplastic material. The hardness ofthe flexible housing 80 is advantageously 20-75 on the Shore A scale,e.g. around 55 on the shore A scale. The hardness of the plate-shapedelement 71 is advantageously 45-100 on the shore D scale, e.g. around 75on the shore D scale.

FIGS. 6a and 6b show detailed cross-sectional views of a firstembodiment and a second embodiment of a flow guiding device partaccording to the invention and provided with attachment parts accordingto the invention.

FIG. 6a shows a first embodiment of the flow guiding device part 70 andthe attachment part 77. It is seen that a tapered section of theattachment part 77 and the plate-shaped element are integrally formed,e.g. as a moulded element. The flexible housing 80 is connected to arecess 83 of the tapered section of the attachment part 77. The flexiblehousing may be glued onto or moulded onto the tapered section. Theflexible housing 80 comprises a circumferential lip 82, which is sealedagainst the surface of the wind turbine blade. This provides a gluecavity 81, which is formed between the surface of the blade, theflexible housing 80 and a lower part of the tapered section of the flowguiding device part 70. A bore or hole 79 is provided through theattachment part 77 and which can communicate with the glue cavity 81such that an adhesive may be filled into the cavity 81 via the bore 79.The flexible housing further comprises a ventilation hole 88, wherebygas or air is able to escape from the cavity 81 during a step ofinjecting an adhesive into the cavity. The ventilation hole 88 may alsoprovide a visual confirmation of the filling process, e.g. when liquidadhesive starts pouring out from the hole, the injection of the adhesivemay be stopped.

FIG. 6b shows a second embodiment of a flow guiding device part 70′ andan attachment part 77′, where like numerals refer to like parts of thefirst embodiment. Therefore, only the difference between the twoembodiments is described. The second embodiment differs from the firstembodiment in that the flexible housing encases a lower part of thetapered section 77′ or the plate-shaped element 70′, such that the gluecavity 81′ is formed between the flexible housing 80 and the surface ofthe blade only.

The lip 82 of the attachment device 77 advantageously has a maximumexternal dimension, such as an outer diameter, of 1-15 cm, or 2-10 cm.Thus, the proximal part of the attachment device 77 may have thismaximum external dimension.

According to one embodiment shown in FIG. 7a , the circumferential lip82 may comprise a substantially flat attachment surface 84 for mountingto the blade. The attachment surface may be provided with apressure-sensitive double adhesive tape 85 for providing a preliminaryattachment to the blade surface. The tape 85 may be provided with aliner 86, which is removed prior to fitting the flexible housing 80 tothe surface of the blade. The liner 86 is advantageously provided with atap so that the liner 86 can be pulled out from the lip 82. Thus, thelip 82 of the flexible housing 80 may be pressed against the surface ofthe blade. Once the device 70 and attachment part 77 is located in thecorrect position, the liner 86 is removed, whereby the lip 82 ispreliminary sealed to the surface of the wind turbine blade and providesthe glue cavity 81, and after which injection of adhesive into thecavity 81 may be carried out.

According to another embodiment shown in FIG. 7b , a circumferential lip182 of the flexible housing has an inclined attachment surface 184.Similar to the embodiment shown in FIG. 7a , the attachment surface maybe provided with a pressure-sensitive double adhesive tape 185 forproviding a preliminary attachment to the blade surface, which in turnis provided with a liner 186. The incline of the attachment surface 184accommodates to the surface of the wind turbine blade, when it ispressed against said surface of the wind turbine blade, which isillustrated with the arrows shown in FIG. 7 b.

FIG. 8 illustrates a step in a method of attaching a surface mounteddevice to the surface of a wind turbine blade according to theinvention. The method comprises a first step of providing the windturbine blade and a second step of providing the surface mounted devicewith an attachment part according to the invention, e.g. one of the twoembodiments shown in FIG. 6. In a third step, the attachment part of thesurface mounted device is positioned on a first discrete area of thesurface of the blade so that a cavity is formed between at least thehousing and the surface of the wind turbine blade. In a fourth step,illustrated in FIG. 8, an adhesive or resin 91 is filled into the gluecavity. Once the glue cavity 81 has been filled with the adhesive,injection is stopped after which the adhesive 91 in a fifth step iscured or hardened so that the surface mounted device 70 is attached tothe surface of the wind turbine blade via an adhesive bonding.

The adhesive 91 is injected into the glue cavity 81 via the bore 79,e.g. via a syringe or a static mixer. The ventilation hole 88 ispreferably located at a proximal part of the flexible housing, such thatadhesive 91 filled into the cavity 81 reaches said ventilation hole 88last. Thereby, the ventilation hole 88 may also be used for visualinspection to check if the cavity has been filled. Alternatively oradditionally, the flexible housing may be made in an at least partiallytransparent material, such that the filling process can be monitored.

The cavity 81 may remain connected to an adhesive reservoir 90 orchamber during the curing or hardening in the fifth step. Thus, if theadhesive 91 shrinks during the hardening, additional liquid adhesivewill be drawn into the cavity and filling the voids. The adhesive 91 ofthe reservoir 90 should of course harden at a later stage than theadhesive in the cavity such that liquid adhesive is not drawn in thewrong direction.

The adhesive 90 may for instance be PU-based, epoxy-based or MMA. It mayalso be a hybrid between the various materials, such as a polymerisablePU mixed in a MMA.

In another embodiment, a micro-environment treatment is carried out inthe cavity prior to the fourth step. The micro-environment treatment mayfor instance be chosen from the group of evacuating the cavity, heatingthe cavity, or a degasification, e.g. via filling the cavity withnitrogen. Thereby, the cavity may be dried before the injection step,which may improve the adhesive bond even further, since moist is removedprior to the injection. This may be carried out via attaching theappropriate tool to the bore 79 or the ventilation hole 88.

As shown in FIGS. 2 and 4, the surface mounted devices areadvantageously flow guiding devices e.g. in form of spoiler devices,which are grouped together to form a flow guiding device group. Themodular construction of this group makes the construction more flexibleand reduces peel forces at the ends of the flow guiding device parts.The individual flow guiding device parts are preferably arranged suchthat the lengthwise directions of the parts are oriented substantiallyin the longitudinal direction of the blade.

FIG. 9 shows a back view of a first embodiment of a flow guiding devicegroup. As can be seen, the group comprises a number of individual flowguiding device parts 170, which mutually are separated by gaps 181. Thegaps 181 between adjacent flow guiding device parts 170 may for instancebe between 5 mm and 30 mm. According to another embodiment (not shown),the flow guiding device parts abut each other.

FIG. 10 shows the flow guiding device parts 170 seen from the top, heredepicted as a proximal part of a plate-shaped element. In the shownembodiment, the gaps 181 between adjacent flow guiding device parts 170are closed by intermediate elements 196 made of a flexible material,such as rubber. In this particular embodiment, the intermediate elements179 are attached to a front surface of the plate-shaped elements 170.This may provide a continuous front surface for the flow guiding devicegroup. However, according to a preferred embodiment, the design does notcomprise any intermediate elements (corresponding to the embodimentshown in FIG. 9).

FIG. 11 shows a second embodiment of flow guiding device parts 270according to the invention. In this embodiment the gaps are also closedby intermediate elements 296 made of a flexible material, such asrubber. In this embodiment, the intermediate parts fill the entire gapbetween the flow guiding device parts 270 and are attached to both afront surface and back surface of the flow guiding device parts 270.

FIG. 12 shows a schematic view of a third embodiment of flow guidingdevice parts 370 according to the invention, seen from the top. In thisembodiment, the flow guiding device parts are alternately arranged infront of and behind other flow guiding device parts, such that the flowguiding device parts form a nearly continuous front surface.

FIG. 13 shows a schematic view of a fourth embodiment of flow guidingdevice parts 470 according to the invention, seen from the top. It canbe seen the flow guiding device parts 470 are staggered in thelongitudinal direction. The back surface of one flow guiding device partmay abut the front surface of a second flow guiding device part, orthere may be a small gap in the transverse direction of the blade.

FIG. 14 shows a schematic view of a fifth embodiment of flow guidingdevice parts 570 according to the invention, seen from the top, which issimilar to the third embodiment with the exception that the flow guidingdevice parts 570 are alternately convex and concave in the longitudinaldirection. In the shown embodiment, two flow guiding device parts arearranged behind the others. However, they may also advantageously bearranged in front of the other flow guiding device parts, therebyobtaining a slightly different overall design. If the flow guidingdevice parts are angled forwards to form a pocket between theplate-shaped element and the blade surface, it is clear that twodifferent types of flow guiding device parts are needed.

The invention has so far been described in relation to surface mounteddevices in form of spoiler devices. However, the attachment parts andmethod according to the method may also be used for attaching othertypes of flow guiding devices to the surface of a wind turbine blade,e.g. serrated trailing edge panels or Gurney flaps.

FIG. 15 shows such an embodiment of a wind turbine blade 610, which isprovided with a plurality of serrated trailing edge panels 670, whichare arranged at the trailing edge of the blade near the blade tip. Asseen in FIG. 16, the serrated trailing edge panel 670 may be providedwith an attachment part, which comprises a flexible housing 681, whichforms a glue cavity 681 between the panel 670 and the blade surface. Thepanel 670 is adhesively attached to the blade by filling the glue cavitywith an adhesive and letting the adhesive cure or harden.

FIG. 17 shows an alternative embodiment of a serrated trailing edgepanel 770, which is provided with three attachment parts, eachcomprising a flexible housing 780 and forming a glue cavity 681 betweenthe panel 770 and the blade surface. The three attachment parts may,seen in a top view, be arranged in a triangle.

In the above embodiments, the flexible housing is described as apre-manufactured element. However, the attachment part or the flexiblehousing is made from a double-adhesive tape or the like. In thefollowing, such embodiments are exemplified for the attachment of aserrated trailing edge panel. However, the flexible housing made ofdouble-adhesive tape may be used for any surface mounted device, such asspoiler devices or the like.

FIG. 18 shows a top view of a first embodiment of a serrated trailingedge panel 870, where the flexible housing 880 of an attachment part ismade from double-adhesive tape. The double-adhesive tape may be appliedto the surface of the wind turbine blade (not shown) as separate parts880 a, 880 b, 880 c, 880 d, which are arranged so that they form acircumferential part. Once the serrated trailing edge panel 870 isarranged on top of the double-adhesive tape, a cavity 881 is formedbetween the surface of the wind turbine blade, the double-adhesive tapeand the serrated trailing edge panel 870. Liquid adhesive may then beinjected into the cavity 881, e.g. via a bore 879 in the serratedtrailing edge panel 879, and the adhesive propagates (illustrated withcontour lines 893) through the cavity 881.

The double-adhesive tape parts 880 a, 880 b, 880 c, 880 d may bearranged so that a small opening 888 is provided in the circumferentialpart, such that a visual confirmation of the filling process may beprovided, e.g. when liquid adhesive starts pouring out from the hole,the injection of the adhesive may be stopped.

FIG. 19 shows a top view of a second embodiment of a serrated trailingedge panel, where the attachment part is made from double-adhesive tape.The double-adhesive tape may be applied to the surface of the windturbine blade (not shown) as separate parts 980 a, 980 b, 980 c, 980 d,which are arranged so that they form a circumferential part. Once theserrated trailing edge panel 970 is arranged on top of thedouble-adhesive tape, a cavity 981 is formed between the surface of thewind turbine blade, the double-adhesive tape and the serrated trailingedge panel 970. The double-adhesive tape parts 980 a, 980 b, 980 c, 980d are arranged so that an opening 979 is provided in the circumferentialpart. Liquid adhesive may then be injected through said opening 979illustrated with contour lines 993.

Liquid adhesive may then be injected into the cavity 881, e.g. via abore 879 in the serrated trailing edge panel 879, and the adhesivepropagates (illustrated with contour lines 893) through the cavity 881.

The double-adhesive tape parts 980 a, 980 b, 980 c, 980 d mayadditionally be arranged so that a second small opening 988 is providedin an opposite side of the circumferential part, such that a visualconfirmation of the filling process may be provided, e.g. when liquidadhesive starts pouring out from the hole, the injection of the adhesivemay be stopped.

In one advantageous embodiment, the double-adhesive tape comprises alayer of compressible material. This provides a viscoelastic housing.The compressible material may for instance be a layer of foam cells,such as acrylic foam. The double-adhesive tape may have a thickness ofat least 0.5 mm, and preferably at least 1 mm. Accordingly, a cavityhaving a height of e.g. 1 mm to 5 mm may be provided.

FIGS. 20-23 illustrate various steps in another embodiment for attachsurface mounted devices, such as spoiler parts, to the surface of a windturbine blade. While it according to the invention is not strictlynecessary to remove the gelcoat for providing a proper bonding for theattachment parts, this may in some circumstances improve the bonding. Ina first step shown in FIG. 20, an area 1065 on the surface of the blademay be prepared for arrangement and mounting of surface mounted devices.This may be carried out by removing the gelcoat in the area 1065.Alternatively, the blade shell may be manufactured with an area void ofgelcoat.

In a next step illustrated in FIG. 21, a template for drilling alignmentholes 1067 is arranged in the area 1065 prepared for arrangement of thesurface mounted devices.

In a next step illustrated in FIG. 22, a plurality of patches 1068 arealigned on top of the alignment holes 1067. The patches 1068 may beprovided with a pin for arrangement in the alignment holes. The patches1068 may be arranged by use of a special tool, which has pre-aligned theorientation of the patches 1068.

In a next step, not illustrated, a gelcoat is applied to the preparedarea 1065 and on top of the patches 1068. After the gelcoat has cured,the patches 1068 may be removed, thereby leaving a plurality of areaswithout gelcoat on the surface of the wind turbine blade.

In a next step, not illustrated, the surface mounted devices arearranged such that the flexible housing and attachment part is arrangedon top of the gelcoat-free areas 1068.

The attachment part of the surface mounted devices may be mechanicallyfixed to the surface of the blade by use of screw attached through theattachment part and screwed into the alignment holes 1067 on the surfaceof the blade.

Such an embodiment is shown in FIG. 23, wherein like reference numeralrefer to like parts of the embodiments shown in FIGS. 6a and 6b .Therefore, only the difference between the embodiment in FIG. 23 andFIG. 6a is described. The embodiment differs in having a bore 1087 for ascrew, and the attachment part is preliminary attached to the surface ofthe blade via a screw (not shown) inserted through the bore 1087 andscrewed into the alignment holes 1067 formed in the surface of theblade. The alignment holes e.g. have a depth of 20 mm.

After the adhesive has been injected into the cavity 1081 and cured, thescrew may be removed. The remaining hole may then be filled with asealant.

The invention has been described with reference to a preferredembodiment. However, the scope of the invention is not limited to theillustrated embodiment, and alterations and modifications can be carriedout without deviating from the scope of the invention.

LIST OF REFERENCE NUMERALS

2 wind turbine 4 tower 6 nacelle 8 hub 10, 610 blade 14 blade tip 16blade root 18 leading edge 20 trailing edge 22 pitch axis 30 root region32 transition region 34 airfoil region 36 pressure side shell 38 suctionside shell 40, 42, 50 Profiled contour 52 Pressure side 54 Suction side56 Leading edge 58 Trailing edge 60 Chord 62 Camber line/median line1065 Area prepared for mounting of surface mounted devices 1067 Templatefor alignment holes 1068 Pads/gel-coat free areas 70, 70′, 170, 270,370, Surface mounted device/flow 470, 570, 670, 770, 870, guiding device970, 1070 71, 71′, 1071 Plate-shaped element 72 Front surface 73 Rearsurface 74 Proximal/lower part of surface mounted device 75 Distal/upperpart of surface mounted device 76 Grid/rib structure 77, 77′ Attachmentpart 78 Grip 79, 79′, 879, 979, 1079 Bore/hole/opening 80, 80′, 680,780, 880, Flexible housing 980, 1080, 81, 81′, 681, 781, 881, Gluecavity 981, 1081 82, 82′, 182, 1082 Circumferential lip 83, 83′, 1083Recess 84, 184 Attachment surface 85, 185 Double adhesive tape 86, 186Liner 1087 Bore for screw 88 Ventilation bore/hole 91 Reservoir 893, 993Propagation front 92 Adhesive 95 Flow guiding device group 196, 296Intermediate elements c Chord length d_(t) position of maximum thicknessd_(f) position of maximum camber d_(p) position of maximum pressure sidecamber f camber r local radius, radial distance from blade root tthickness

1. A wind turbine blade (10, 610) for a rotor of a wind turbine (2)having a substantially horizontal rotor shaft, said rotor comprising ahub (8), from which the wind turbine blade (10, 610) extendssubstantially in a radial direction when mounted to the hub (8), thewind turbine blade (10, 610) having a longitudinal direction (r) with atip end (14) and a root end (16) and a transverse direction, the windturbine blade (10) further comprising: a profiled contour (40, 42, 50)including a pressure side and a suction side, as well as a leading edge(18) and a trailing edge (20) with a chord having a chord lengthextending there between, the profiled contour, when being impacted by anincident airflow, generating a lift, wherein a surface mounted device(70, 70′, 170, 270, 370, 470, 570, 670, 770) is attached to a surface ofthe wind turbine blade (10), wherein the surface mounted device (70,70′, 170, 270, 370, 470, 570, 670, 770) is attached to the surface ofthe wind turbine blade (10, 610) via at least a first attachment part(77, 77′), which is connected to a part of the surface mounted device(70, 70′, 170, 270, 370, 470, 570, 670, 770), characterised in that theattachment part (77, 77′) comprises a flexible housing (80, 80′, 680,780) that forms a cavity (81, 81′, 681, 781) between at least thehousing (80, 80′, 680, 780) and the surface of the wind turbine blade(10, 610), and wherein the cavity (80, 80′, 680, 780) is filled with anadhesive that provides an adhesive bonding to the surface of the windturbine blade (10, 610).
 2. A wind turbine blade according to claim 1,wherein the flexible housing is made of a first material and the surfacemounted device made of a second material, wherein a hardness of thefirst material is smaller than the hardness of the second material.
 3. Awind turbine blade according to claim 1, wherein the flexible housing ismade of an elastomer material.
 4. A wind turbine blade according toclaim 1, wherein the attachment part is tapered from a proximal part toa distal part of the attachment part, e.g. being bell-shaped, conicalshaped, or frusto-conical shaped.
 5. A wind turbine blade according toclaim 1, wherein the surface mounted device is a flow guiding device,such as a spoiler device or a Gurney flap.
 6. A wind turbine bladeaccording to claim 1, wherein the surface mounted device comprises aplate-shaped element, which protrudes from the surface of the windturbine blade.
 7. A wind turbine blade according to claim 1, wherein thesurface mounted device is arranged on the pressure side of the blade. 8.A wind turbine blade according to claim 1, wherein the surface mounteddevice is curved in a lengthwise direction of the device.
 9. A windturbine blade according to claim 8, wherein a lengthwise radius ofcurvature of the surface mounted device varies from a proximal part ofthe surface mounted device to a distal part of the surface mounteddevice, e.g., wherein the radius of curvature increases from theproximal part to the distal part of the surface mounted device,alternatively wherein the radius of curvature decreases from theproximal part to the distal part of the surface mounted device.
 10. Awind turbine blade according to claim 1, wherein the surface mounteddevice is reinforced with a grid or rib structure.
 11. A wind turbineblade according to claim 1, wherein the surface mounted device may beangled towards the leading edge of the blade so as to provide a pocketbetween the surface mounted device and the surface of the blade, saidpocket facing towards the leading edge of the blade.
 12. A wind turbineblade according to claim 1, wherein the flexible housing is made of adouble-adhesive tape.
 13. A wind turbine blade according to any claim12, wherein the double-adhesive tape forms a circumferential partbetween the surface of the wind turbine blade and the surface mounteddevice, and which forms a cavity between the double-adhesive tape, thesurface of the wind turbine blade and a part of the surface mounteddevice.
 14. A wind turbine blade according to claim 12, wherein thedouble-adhesive tape comprises a layer of compressible material.
 15. Awind turbine blade according to claim 14, wherein the compressiblematerial is a layer of foam cells, such as acrylic foam.
 16. A windturbine blade according to claim 12, wherein the double-adhesive tapehas a thickness of at least 0.5 mm, and preferably at least 1 mm.
 17. Awind turbine blade according to claim 12, wherein the adhesive tape hasa thickness of maximum 10 mm, or maximum 7 mm, or maximum 5 mm.
 18. Aflow guiding device, which is adapted to be attached to the surface of awind turbine blade, via at least a first attachment part, characterisedin that the attachment part comprises a flexible housing that is adaptedto form a cavity between at least the housing and the surface of thewind turbine blade, the cavity being adapted to be filled with anadhesive that provides an adhesive bonding to the surface of the windturbine blade.
 19. A method of attaching a surface mounted device to asurface of a wind turbine blade, wherein the wind turbine blade has alongitudinal direction with a tip end and a root end and a transversedirection, wherein the wind turbine blade further comprises a profiledcontour including a pressure side and a suction side, as well as aleading edge and a trailing edge with a chord having a chord lengthextending there between, the profiled contour, when being impacted by anincident airflow, generating a lift, wherein the method comprises thesteps of: a) providing the wind turbine blade, b) proving a device formounting on the surface of the blade, the device having at least oneattachment part connected to a part of the surface mounted device,wherein the attachment part comprises a flexible housing adapted to forma cavity between at least the housing and the surface of the windturbine blade, c) positioning the attachment part on a first discretearea of the surface of the blade so that a cavity is formed between atleast the housing and the surface of the wind turbine blade, d)injecting an adhesive or resin into the cavity, and e) curing orhardening the adhesive or resin so that the device is attached to thesurface of the wind turbine blade via an adhesive bonding.
 20. A methodaccording to claim 19, wherein the attachment part comprises acircumferential lip for attaching to the surface of the wind turbineblade, e.g. wherein the circumferential lip has a substantially flatattachment surface for mounting to the blade, optionally an inclinedattachment surface.
 21. A method according to claim 19, wherein thecircumferential lip is provided with an adhesive, such as an adhesivetape, e.g. a pressure-sensitive double-adhesive tape, for providing apreliminary attachment to the blade surface.
 22. A method according toclaim 19, wherein the attachment part prior to step d) is mechanicallyfixed to the surface of the wind turbine blade, e.g. via a screwconnected through the attachment part and to an alignment hole formed inthe surface of the wind turbine blade.
 23. A method according to claim19, wherein a micro-environment treatment is carried out in the cavityprior to step d), e.g. wherein the micro-environment treatment is chosenfrom the group of evacuating the cavity, heating the cavity, or adegasification, e.g. via filling the cavity with nitrogen.
 24. A methodaccording to claim 19, wherein the flexible housing is provided with abore or hole from the cavity to an exterior.
 25. A wind turbine bladefor a rotor of a wind turbine having a substantially horizontal rotorshaft, said rotor comprising a hub, from which the wind turbine bladeextends substantially in a radial direction when mounted to the hub, thewind turbine blade having a longitudinal direction with a tip end and aroot end and a transverse direction, the wind turbine blade furthercomprising: a profiled contour including a pressure side and a suctionside, as well as a leading edge and a trailing edge with a chord havinga chord length extending there between, the profiled contour, when beingimpacted by an incident airflow, generating a lift, wherein a surfacemounted device is attached to a surface of the wind turbine blade,wherein the surface mounted device is attached to the surface of thewind turbine blade via at least a first attachment part, which isconnected to a part of the surface mounted device, characterised in thatthe attachment part comprises a flexible housing made of adouble-adhesive tape that forms a cavity between at least the housing,the surface of the wind turbine blade, and a part of the surface mounteddevice, and wherein the cavity is filled with an adhesive that providesan adhesive bonding to the surface of the wind turbine blade.
 26. A windturbine blade according to claim 25, wherein the double-adhesive tapecomprises a layer of compressible material.
 27. A wind turbine bladeaccording to claim 26, wherein the compressible material is a layer offoam cells, such as acrylic foam.
 28. A wind turbine blade according toclaim 25, wherein the double-adhesive tape has a thickness of at least0.5 mm, and preferably at least 1 mm.
 29. A wind turbine blade accordingto claim 25, wherein the adhesive tape has a thickness of maximum 10 mm,or maximum 7 mm, or maximum 5 mm.
 30. A method of attaching a surfacemounted device to a surface of a wind turbine blade, wherein the windturbine blade has a longitudinal direction with a tip end and a root endand a transverse direction, wherein the wind turbine blade furthercomprises a profiled contour including a pressure side and a suctionside, as well as a leading edge and a trailing edge with a chord havinga chord length extending there between, the profiled contour, when beingimpacted by an incident airflow, generating a lift, wherein the methodcomprises the steps of: a) providing the wind turbine blade, b)arranging double-adhesive tape on the surface of the wind turbine bladeso as to form a circumferential part of an attachment part c) arranginga device for mounting on the surface of the blade on the double-adhesivetape so that a cavity of an attachment part is formed between at leastby the double-adhesive tape, the surface of the wind turbine blade, anda part of the device, d) injecting an adhesive or resin into the cavity,and e) curing or hardening the adhesive or resin so that the device isattached to the surface of the wind turbine blade via an adhesivebonding.